FLAP, 5-lipoxygenase activating protein, plays a critical role in the production of leukotrienes by the 5-lipoxygenase (5-LO) pathway. In particular, FLAP mediates the transfer of the substrate, arachidonic acid, released from membrane phospholipids to the active site of 5-LO. Leukotrienes are lipid mediators released by leukocytes, in particular neutrophils, eosinophils, mast cells and monocyte/macrophages. They belong to the wider class of lipid mediators known as eicosanoids, formed from arachidonic acid released from cell membranes. Two distinct classes of leukotriene exist, LTB4 and CysLTs (LTC4, LTD4 and LTE4). Functions of LTB4 include chemo-attraction and activation of leukocytes, inhibition of neutrophil apoptosis, and activation of adhesion molecule expression. Such effects are mediated through binding to one of two distinct G protein-coupled receptors (BLT1 and BLT2) which differ in their affinity and specificity for LTB4. Cysteinyl leukotrienes have vaso-active properties and can affect blood flow and vasopermeability, actions that are mediated by two CysLT receptors, CysLT1 and CysLT2.
To initiate leukotriene biosynthesis, 5-LO translocates to intracellular membranes such as the nuclear membrane where it interacts with FLAP. Arachidonic acid released from membrane phospholipids by cytoplasmic PLA2 (cPLA2) is transferred via FLAP to 5-LO which then stereospecifically incorporates oxygen at the fifth carbon position, with the formation of 5(S)-HpETE. This is subsequently converted by 5-LO to LTA4, the common precursor for leukotriene B4 (LTB4) and the cysteinyl leukotrienes (LTC4, LTD4 and LTE4). The conversion of LTA4 to LTB4 is mediated by LTA4 Hydrolase (LTA4H), a zinc-dependent epoxide hydrolase. Formation of cysteinyl leukotrienes involves conjugation of LTA4 to glutathione, mediated by LTC4 synthase in cell membranes in association with FLAP, and the resulting LTC4 may be further processed to LTD4 and LTE4 via peptidase activities.
Compounds that inhibit the function of either 5-LO or FLAP can result in the inhibition of leukotriene production. FLAP inhibitors bind directly to FLAP in cell membranes and prevent leukotriene biosynthesis by preventing the membrane translocation of 5-LO and/or the supply of arachidonic acid substrate to its active site. In this way, inhibition of FLAP prevents the production of both LTB4 and cysLTs by inhibiting production of the common precursor LTA4. Distinct from 5-LO inhibitors, FLAP inhibitors do not directly suppress oxidation of arachidonic acid by 5-LO and do not inhibit leukotriene production in lysed cell extracts.
Despite the availability of drugs that deal with risk factors such as high cholesterol levels and elevated blood pressure, further treatment options are needed to reduce atherosclerotic cardiovascular disease and its sequellae. The role of lipid deposition in the formation of atherosclerotic plaques is well-established. However, another key factor in atherogenesis is inflammation, including both the recruitment of inflammatory cells to atherosclerotic lesions and their activation within plaques. Pharmacological approaches that target inflammation could therefore provide a novel approach to treating patients with atherosclerosis. Inhibition of leukotriene production by means of administering a FLAP inhibitor is one such approach.
Another risk factor associated with cardiovascular disease is microvascular dysfunction. By attenuating leukocyte activation and interaction with the microvasculature in addition to reducing the production of vasoactive cysteinyl leukotrienes, pharmacological inhibition of FLAP could improve microvascular function in cardiovascular disease patients.
A link between FLAP, 5-LO pathway activity, leukotriene production and cardiovascular disease is supports, by the following lines of evidence: 1) expression and activity of the 5-LO pathway increases in association with atherosclerotic plaque progression and symptoms of plaque instability that could cause plaque rupture and thrombosis leading to myocardial infarction (MI). (Spanbroek et al (2003) PNAS 100, 1239; Cipollone et al (2005) ATVB 25, 1665); 2) leukotriene levels in blood and urine are elevated in the period following a recent acute coronary syndrome (ACS) event (Sanchez-Gala et al (2009) Cardiovascular Research 81, 216; Carry et al (1992) Circulation 85, 230); 3) genetic haplotypes in the FLAP (ALOX5AP) gene are significantly associated with the risk of myocardial infarction (Helgadottir et al (2004) Nature Genetics 36, 233).
Many companies over the course of the last few decades have pursued FLAP as a target, and patent filings associated with these efforts are summarized in various publications. See e.g., Pergola & Werz, Expert Opin. Ther. Patents (2010) 20(3); and Hofmann & Steinhilber Expert Opin. Ther. Patents, (2013) 23(7) and Whatling Bioorg. Med Chem. Lett. (2015) 25(2607). However, this application presents a new class of compounds distinct from these prior patent filings.
The instant application addresses the large unmet need by providing compounds, compositions and methods for the treatment or prevention of cardiovascular disease and related conditions.